..and doing the opposite.
[Update: yes, I realize that this isn't entirely true. But it's pithy, and it's mostly true. Most of the unhappiness in my life has been caused when I've allowed myself to indulge in short term pleasure rather than doing the work that I know is necessary to achieve my long term goals. For example, I want to have a lean, muscular body. A muscular body and low body fat ratios (in combination with a high nutrition diet) are correlated with longevity and good health. Yet when I feel anxious or bored, I eat chocolate chip cookies and Doritos. Although they provide a brief and certain pleasure, overall, whenever I indulge, it makes me feel even more undisciplined and unhappy.
Conversely, the times when I have felt the most satisfied have been those times when I have fought against my natural inclination. For example, I used to be extremely shy. But after reading how Albert Ellis overcame his own shyness, I began forcing myself to introduce myself to women I found attractive whenever I could -- at bookstores, parties, grocery stores, etc. I've met several very attractive women that way. Even when I was rebuffed, I felt good, because I had overcome my fear and had taken a chance. I'm no social butterfly even now, but I would feel comfortable introducing myself to any woman I found attractive.
On the whole, I think most people indulge in short term pleasures at the expense of long term goals far more often than they do the reverse. So whenever faced with a decision about what to do, l think people would generally be happier if they did what they didn't feel like doing. ]